Review of the proton exchange membranes for fuel cell applications

The state-of-the-art of polymer electrolyte membrane fuel cell (PEMFC) technology is based on perfluorosulfonic acid (PFSA) polymer membranes operating at a typical temperature of 80 °C. Some of the key issues and shortcomings of the PFSA-based PEMFC technology are briefly discussed. These include water management, CO poisoning, hydrogen, reformate and methanol as fuels, cooling, and heat recovery. As a means to solve these shortcomings, high-temperature polymer electrolyte membranes for operation above 100 °C are under active development. This treatise is devoted to a review of the area encompassing modified PFSA membranes, alternative sulfonated polymer and their composite membranes, and acid−base complex membranes. PFSA membranes have been modified by swelling with nonvolatile solvents and preparing composites with hydrophilic oxides and solid proton conductors. DMFC and H2/O2(air) cells based on modified PFSA membranes have been successfully operated at temperatures up to 120 °C under ambient pressure...

/pdf/approaches-and-recent-development-of-polymer-electrolyte-1glbhokzz9.pdf

Approaches and Recent Development of Polymer Electrolyte Membranes for Fuel Cells Operating above 100 °C

Many currently producing shale-gas reservoirs are overmature oil-prone source rocks. Through burial and heating these reservoirs evolve from organic-matter-rich mud deposited in marine, lacustrine, or swamp environments. Key characterization parameters are: total organic carbon (TOC), maturity level (vitrinite reflectance), mineralogy, thickness, and organic matter type. Hydrogento-carbon (HI) and oxygen-to-carbon (OI) ratios are used to classify organic matter that ranges from oil-prone algal and herbaceous to gas-prone woody/coaly material. Although organic-matter-rich intervals can be hundreds of meters thick, vertical variability in TOC is high ( 50% of the total porosity, and these pores may be hydrocarbon wet, at least during most of the thermal maturation process. A full understanding of the relation of porosity and gas content will result in development of optimized processes for hydrocarbon recovery in shale-gas reservoirs.

/pdf/from-oil-prone-source-rock-to-gas-producing-shale-reservoir-1x2ewnfevi.pdf

From Oil-Prone Source Rock to Gas-Producing Shale Reservoir - Geologic and Petrophysical Characterization of Unconventional Shale Gas Reservoirs

In this review, we have examined the different models for polymer-electrolyte fuel cells operating with hydrogen. The major focus has been on transport of the various species within the fuel cell. The different regions of the fuel cell were examined, and their modeling methodologies and equations were elucidated. In particular, the 1-D fuel-cell sandwich was discussed thoroughly because it is the most important part of the fuel-cell assembly. Models that included other effects such as temperature gradients and transport in other directions besides through the fuel-cell sandwich were also discussed. Models were not directly compared to each other; instead they were broken down into their constitutive parts. The reason for this is that validation of the models is usually accomplished by comparison of simulation to experimental polarization data (e.g., Figure 3). However, other data can also be used such as the net flux of water through the membrane. In fitting these data, the models vary not only in their complexity and treatments but also in their number and kind of fitting parameters. This is one reason it is hard to justify one approach over another by just looking at the modeling results. In general, it seems reasonable that the more complex models, which are based on physical arguments and do not contain many fitting parameters, are perhaps closest to reality. Of course, this assumes that they fit the experimental data and observations. This last point has been overlooked in the validation of many models. For example, a model may fit the data very well for certain operating conditions, but if it does not at least predict the correct trend when one of those conditions is changed, then the model is shown to be valid only within a certain operating range. This review has highlighted the important effects that should be modeled. These include two-phase flow of liquid water and gas in the fuel-cell sandwich, a robust membrane model that accounts for the different membrane transport modes, nonisothermal effects, especially in the directions perpendicular to the sandwich, and multidimensional effects such as changing gas composition along the channel, among others. For any model, a balance must be struck between the complexity required to describe the physical reality and the additional costs of such complexity. In other words, while more complex models more accurately describe the physics of the transport processes, they are more computationally costly and may have so many unknown parameters that their results are not as meaningful. Hopefully, this review has shown and broken down for the reader the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled.

Modeling transport in polymer-electrolyte fuel cells.

Modelling the performance of membrane nanofiltration - critical assessment and model development

A two-dimensional, electrokinetic transport model that incorporates ionic hydration, orientation of solvent molecules by an applied electric field, and solvent dipole-dipole interactions is developed. The model is used to simulate equilibrium and transport experiments for perfluorosulfonic acid membranes containing aqueous alkali metal sulfate solutions. The membrane is modeled as an array of cylindrical pores. Solution of the mathematical model requires that the membrane porosity, water partition coefficient, coion partition coefficient, water diffusion coefficients, and coion and counterion diffusion coefficients be known. Membrane coion and counterion diffusion coefficients were determined from free solution equivalent conductance data. All other parameters were determined experimentally for a Nafion (of E. I. du Pont de Nemours Inc.) cation-exchange membrane and five 0.1 M alkali metal sulfate solutions. Experimental radiotracer data for coion absorption as well as for coion and water transport are compared with theoretical predictions to test the accuracy of the model.

Development of a space‐charge transport model for ion‐exchange membranes

One of the primary obstacles to be overcome for the development of economical fuel cells is the high cost of the membrane electrolyte. The currently favoured polymer electrolytes consist of poly(tetrafluoroethylene) backbone structures and poly(perfluorosulphonic acid) side chains. In an effort to find lower cost membranes, some radiation-grafted copolymer membranes were investigated. All the membranes contained poly(styrenesulphonic acid) side chains. Three different backbone polymer structures were studied: low-density poly(styrene), poly(tetrafluoroethylene)/poly(perfluoropropylene), and poly(tetrafluoroethylene). The results indicate that the membrane consisting of a poly(tetrafluoroethylene)/poly(styrenesulphonic acid) copolymer is a promising candidate as a fuel-cell electrolyte.

Analysis of radiation-grafted membranes for fuel cell electrolytes

“Many siliciclastic oil and gas reservoirs contain significant volumes of recoverable hydrocarbons in intervals whose average bed thickness is below the resolution of conventional well-logging tools. In-place hydrocarbon volumes are difficult to evaluate accurately in these thin-bedded reservoirs.

The authors conducted research on thin-bed evaluation methods during the years 1995-1998 and developed a set of methods and practices that have been used worldwide by ExxonMobil since then. The present book describes these methods in the context of an integrated formation evaluation approach for thin-bedded reservoirs. The description is intended to provide useful information for both geoscience generalists and petrophysical specialists.”

Angel G. Guzman-Garcia

Papers

Development of a space‐charge transport model for ion‐exchange membranes

Analysis of radiation-grafted membranes for fuel cell electrolytes

Petrophysical Evaluation of Hydrocarbon Pore-Thickness in Thinly Bedded Clastic Reservoirs

A Systematic Approach To Evaluate Hydrocarbons In Thinly Bedded Reservoirs

The response of straight and circular fins to fluid temperature changes